Locating people, vehicles employees, etc. has become a matter of increased importance over the last several years, especially through the medium of a mobile phone. Much interest in determining mobile phone position was prompted by the Federal Communications Commission (FCC) through its edict to create the wireless Enhanced 911 system (E911) by November 2005.
Several technologies are available and have been proposed for mobile station (e.g. mobile phone, personal digital assistant (PDA) with telecommunications capability, portable computer with telecommunications capability, pager etc.) position determination ranging from use of the global positioning systems (GPS) to phone network-based solutions. Fingerprinting provides another approach to determining the position of a mobile station.
Radio frequency signal characteristics associated with various regions in a signal transmission area are collected in a database. Each grouping of signal characteristics for a region is known as a fingerprint. Typically, the position of a mobile station is determined by comparing a RF data sample collected by the mobile station to fingerprint data in the database. The mobile station's position is determined to lie in the area corresponding to a fingerprint data point of highest correlation to the RF data sample.
The comparison is made by a server holding the fingerprint data. If the comparison were to be accomplished at a mobile station, in accordance with conventional practices, a significant amount of data would have to be downloaded from a network-based database to the mobile station. Fingerprinting requires multiple measurements to be taken from different base stations or cell sites, e.g., base station transceivers (BTSs), at different times of day to capture short-term signal variation (Rayleigh fading, etc.) and variations in network load (capacity) in an effort to capture each fingerprint calibration point for a fingerprint database. Consequently, downloading the fingerprint database to the mobile station would likely be infeasible.
Received signal strength indicator (RSSI) has been used in connection with network planning and fingerprinting by Ekahau, Inc. Radio network sample points are collected from different site locations. Each sample point contains RSSI data together with related map coordinates which are stored in a database for position tracking of persons, assets, equipment, etc. within a Wi-Fi network (802.11a/b/g).
However, this Wi-Fi based Ekahau system is for small applications wherein a program run on a server calculates position determinations and interacts with a client device (i.e., laptop computer, personal digital assistant (PDA), Wi-Fi Tag, etc.) in connection with an application program for recording field data (e.g., RSSI data). The position determination data returned can include the speed, heading, building floor and grid location of client device. For larger scale applications, several U.S. wireless carriers determine a mobile phone's location using RSSI measurements made from and by nearby BTSs.
Triangulation techniques can result in duplicative calculations at a network server which can unnecessarily burden the system, especially in heavily trafficked networks. While not subject to many of the problems associated with other position identifying technologies, fingerprinting requires substantial work in data collection and is most feasible in highly populated, highly concentrated metropolitan areas. However, fingerprinting benefits from the collection of multi-path signal data which arises through indirect signal paths from transmitter to receiver. A need exists to seize on the benefits of fingerprinting in a manner that improves current RSSI position measurement techniques.